Controlling The Burn/Preventing Fire Extension
First as stated earlier we must cover all avenues of fire extension regarding unwanted holes and cut-aways through the walls and ceilings of a room. Next we need to establish the specific area in the room where the main body of ignitable combustibles will be. Remember that combustibles piled or placed in the center of a room will burn more freely and faster possibly providing a loss of control by the instructors in regards to the fires speed of growth. Whereas placing furnishings and combustibles closer to walls such as in the corner of a room will allow the entrainment of air into the fire more slowly and evenly. When we say in the corner of a room we do not mean right up against the walls but allowing for adequate space around the materials so as to be more away from the walls. This allows for better entrainment of air currents and a more evenly controlled plume of heat and fire gases up into the room to allow it to move across a ceiling towards an entryway. This is what is known as intentional fire directing and controlled fire behavior allowing for a more timed and directionally controlled event when incorporating fire suppression training. In order to do this we need to apply protection to surfaces within the room so as to prevent or delay the heat, gases and flames from attacking the infrastructure of the structure. In other words, the framing and interior spaces of walls and attics must be protected to delay their involvement. That is unless we would like fire to travel to these areas in which case this would then not be conducive to a safe and proper burn for live fire training.
Back to the placement of the drywall. Pick the corner of the room where the burn will take place. Cover this area at the ceiling, squaring in the drywall into the corners above at the ceiling and on the upper walls at the corners. The best way to attain the positioning of the drywall is to be sure to cut it into even 4x4 sections placing them like large tiles. Behind the combustibles in the corner at the base of each joining wall should be placed a 4x4 piece of drywall. Add another directly on top of those. Add an additional 4x4 to each side of those and then another to each side of those on the walls on each side. This will bring you a covering distance of approximately 12 feet of the upper wall of a room. If the room is smaller cut the last piece to fit. Depending on the height of the room will depend how high you need to continue to go up. Two 4x4 sections put one directly over the other will usually equal the height of a room with some over lap at the center seam.
The ceiling should be covered in a square made up of 4x4, pieces off the corner of the room with a single row of drywall pieces running along the sides of the ceiling where it meets the wall touching the other drywall pieces on the upper walls. Place a pair of 4x4 pieces touching the square pieces formed on the ceiling towards the direction of the doorway or entryway to the room. You are not covering the whole ceiling just the area of assumed fire travel. Do this until you reach the doorway fitting the pieces at the ceiling right up to the doorway header. Now apply one 4x4 piece of drywall to each side of the door jamb trim at the top part of the wall where it meets the ceiling. Fill in a piece above the door on the wall to the ceiling. You will also apply this to the outside area of the door jamb area on the wall at the ceiling. You will then place two 4x4 pieces of drywall on the ceiling at the wall right over the doorway. You will then cut pieces of drywall to fit and cover the entire header of the doorway inside and outside the doorway.
By preparing a room in this fashion you will be able to provide repeated burns and less chance of allowing fire into the structure. You will also provide more realism within the structure regarding fire travel, smoke conditions, smoke travel, heat currents, dropdown conditions from the drywall application during water application as well as ember dropdown and drywall dropdown. All this can be obtainable when done properly which will reduce the damage and possibilities of fire extension into the structure. Remember that proper size ventilation holes must be pre-cut above fire areas on the roof which will also allow for less damage and more productive burns.